I think there are still too many other differences to consider Northrop/Raytheon/Lockheed mercenaries. They're the core of the US military-industrial complex, but I still think they're effectively an arm of the US military and are much closer to contractors than mercenaries.
A company like Blackwater is much closer to actual mercenaries - they're trying to build their own private, independent military-industrial complex, in a sense, by selling their services to existing complexes.
If your point is that some self-described 'defense contractors' are arms merchants rather than mercenaries, then I agree. 'Defense contractor' is still a euphemism in that case however.
For this matter, Department of Defense is also a euphemism. It used to have the more honest name Department of War until that was changed in the late 1940s.
A company like Blackwater is much closer to actual mercenaries - they're trying to build their own private, independent military-industrial complex, in a sense, by selling their services to existing complexes.